A Mechanical Approach for Evaluating the Distribution of Confinement Pressure in FRP-Wrapped Rectangular Columns

In recent decades, fiber reinforced polymer (FRP) wrapping has become a common technique to retrofit reinforced concrete (RC) columns. Numerous research works have sought to verify analytically and experimentally its effectiveness in terms of enhancement of axial load bearing capacity and ductility. These studies highlighted that in the case of sharp-cornered sections, the maximum allowable confinement pressure is limited by premature failure at corners and, consequently, stress in the FRP, as well as the distribution of the confinement pressure, is not uniform. The prediction of this phenomenon is not straightforward, and existing theoretical studies propose complex numerical simulations, whereas technical codes provide simplified or empirical relationships for its assessment. This paper presents an analytical model for the evaluation of the effective distribution of confinement pressure in FRP confined concrete members with rounded corners. The model allows considering the interaction with the concrete core and different brittle failure modes, including FRP rupture and debonding. It leads to determining the distribution of the confinement pressure along the section. Results are compared with those achieved by finite-element (FE) analyses and with numerical and experimental data available in the literature. Good agreement is obtained in all cases, showing the reliability of the proposed model.